The present invention utilizes a solid electrolyte membrane in separation of hydrogen and production of electricity (a fuel cell). The Nernst equation describes the behavior of such a system, as follows. When two media with different partial pressures, P.sub.1 and P.sub.2, of a particular substance present in both media are separated by a solid electrolyte (ionic conductor) and conducting electrodes are attached to both sides of the ionic conductor, an EMF is generated which is related to the partial pressures as follows: ##EQU1## where R is the gas constant, T is absolute temperature, F is the Faraday constant, E.sub.o is the standard oxidation-reduction potential difference, EMF is electromotive force, and n is the number of electrons per molecule of product from the overall cell reaction.
If the system described by the above equation behaves nonideally, the partial pressures must be replaced by fugacities. Another factor which may need to be considered in regard to a particular system is the rate of dissociation to form the ions which pass through the solid electrolyte. This may be a limiting factor to the transfer of ions through the electrolyte. The rate of dissociation can be calculated by means of the equilibrium constant for the dissociation reaction.
In a majority of cases, the admixture of an organic compound, especially in a polymeric state, with an inorganic compound, results in a phase separation due to the fact that the two systems are immiscible in nature. However, we have discovered that a thin film polymer-blend membrane may be fabricated by admixing the organic and inorganic components discussed herein; the resulting substance is not merely a physical mixture but exhibits a degree of interaction, that is, some amount of chemical interaction exists. Substances which are permeable by gases in a selective manner are known and utilized in a variety of applications. A membrane formed in accordance with the present disclosure is substantially impermeable to ions and gases, including hydrogen gas, but does allow hydrogen ions to pass through it. It should be noted that the membrane is not expected to be totally impermeable and that substances in addition to hydrogen ion may pass through it. Permeability experimentation has not been done, except to the extent indicated herein. For background information relating to the principles of the present invention, reference may be made to the book Solid Electrolytes and Their Applications, edited by Subbarao, Plenum Press, 1980.
Low mechanical strength has been a common problem when attempting to apply permselective membranes. The present invention provides a membrane whose mechanical strength is increased by compositing it with other materials, but whose desirable properties are not lost as a result of doing so.
In a simple hydrogen-oxygen fuel cell, the fuel gas is hydrogen and the oxidant gas is oxygen. Hydrogen dissociates into hydrogen ions and electrons at the catalyst on the fuel gas side of the membrane. The hydrogen ions pass through the electrolyte element while the electrons flow through the external circuit, doing electrical work before forming water by combining with, at the catalytic agent on the oxidant gas side of the membrane, hydrogen ions which passed through the membrane and oxygen. A flow of gases is normally maintained for continuous operation of the fuel cell. The maximum voltage which can be produced by a fuel cell is a thermodynamic function of the fuel and oxidant. For a hydrogen-oxygen fuel cell, the theoretical EMF is 1.23 volts. The actual voltage will be less due to losses within the cell. The current produced is controlled by such considerations as the rate at which the electrochemical reactions proceed, the electrolyte thickness, and the catalyst surface area. In a simple hydrogen-oxygen cell, the partial pressure term of the Nernst equation becomes partial pressure of water divided by the quantity partial pressure of hydrogen times square root of partial pressure of oxygen.
When producing hydrogen by means of the electrochemical process of this invention, the amount produced is generally in accordance with the parameters discussed above: the Nernst equation and, where applicable, the dissociation equilibrium constant. The rate at which separation takes place may be increased by adding means to generate an EMF to the external circuit. That is, a difference in partial pressures is sufficient to provide the driving force for hydrogen ion transport through the membrane, but applying an externally generated driving force will increase hydrogen ion flux. In the practice of all embodiments of this invention, it should be noted that exact adherence to theoretical relationships is not required of commercially used methods and apparatus.